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Intel Open Source License 

Copyright (c) 2002-2011 Intel Corporation. All rights reserved.
 
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modification, are permitted provided that the following conditions are
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Redistributions of source code must retain the above copyright notice,
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in binary form must reproduce the above copyright notice, this list of
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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END_LEGAL */

#include <stdio.h>
#include <pthread.h>
#include <stdlib.h>
#include <unistd.h>
#include <syscall.h>
#include <linux/unistd.h> 
#include <asm/ldt.h> 
#include <errno.h>
#include <string.h>
#include <sys/utsname.h>

#ifndef __NR_set_thread_area
#   define __NR_set_thread_area 243
#endif
#ifndef __NR_get_thread_area
#   define __NR_get_thread_area 244
#endif
#ifndef SYS_set_thread_area
#   define SYS_set_thread_area __NR_set_thread_area
#endif
#ifndef SYS_get_thread_area
#   define SYS_get_thread_area __NR_get_thread_area
#endif

#define NTHREADS 4

struct UserDesc
{
    UserDesc(): _entry_number(0), _base_addr(0), _val1(0), _val2(0) {}
    unsigned int  _entry_number;
    unsigned int  _base_addr;
    unsigned int  _val1;
    unsigned int  _val2;
};


# define TLS_GET_GS_REG() \
  ({ int __seg; __asm ("movw %%gs, %w0" : "=q" (__seg)); __seg & 0xffff; })

#  define TLS_SET_GS_REG(val) \
  __asm ("movw %w0, %%gs" :: "q" (val))

# define TLS_GET_FS_REG() \
  ({ int __seg; __asm ("movw %%fs, %w0" : "=q" (__seg)); __seg & 0xffff; })

#  define TLS_SET_FS_REG(val) \
  __asm ("movw %w0, %%fs" :: "q" (val))

char buf[NTHREADS][3000];
unsigned int mainThreadAddress[8192];

#define GDT_NUM_OF_ENTRIES   3
#define GDT_ENTRIES 16


unsigned int GdtFirstEntry()
{
    static int first = 0;
    if (first) return first;

    UserDesc thrDescr;

    for (int i=0; i< GDT_ENTRIES; i++)
    {
        thrDescr._entry_number = i;
        int res = syscall(SYS_get_thread_area, &thrDescr);
        if ((res == 0) || (errno != EINVAL))
        { 
            first = i;
            return first;
        }
    }
    fprintf(stderr, "First GDT entry is not found\n");
    exit(-1);
}

void * thread_func (void *arg)
{
    unsigned long thread_no = (unsigned long)arg+1;

    unsigned int gs_value = TLS_GET_GS_REG();
    sprintf(buf[thread_no-1],"gs value for thread %ld is 0x%x\n", thread_no, gs_value );

	unsigned int gdtEntryMin = GdtFirstEntry();
	unsigned int gdtEntryMax = gdtEntryMin + GDT_NUM_OF_ENTRIES - 1;
	
    for (unsigned int i=gdtEntryMin; i<=gdtEntryMax+1; i++)
    {
        UserDesc thrDescr;
        thrDescr._entry_number = i;
        int res = syscall(SYS_get_thread_area, &thrDescr);
        if (res == 0)
        {
            if (thrDescr._base_addr != mainThreadAddress[i])
                sprintf(buf[thread_no-1],"%s thread %d: base addr for entry %d has been changed by clone()\n", 
                    buf[thread_no-1], thread_no, i);
            else
               sprintf(buf[thread_no-1],"%s thread %d: base addr for entry %d is equal to the same entry in main thread\n", 
                    buf[thread_no-1], thread_no, i); 
        }
        else
        {
           sprintf(buf[thread_no-1],"%s thread %d: SYS_get_thread_area failed for entry %d with error: %s\n", 
           buf[thread_no-1], thread_no, i, strerror(errno));
        }
        
    }

    return 0;
}

int main (int argc, char *argv[])
{
    UserDesc thrDescr;
    pthread_t h[NTHREADS];

    for (unsigned int i=0; i<8192; i++)
    {
        mainThreadAddress[i] = 0;
    }
    
    thrDescr._entry_number = GdtFirstEntry();
    int res = syscall(SYS_get_thread_area, &thrDescr);
    if (res != 0)
    {
        printf("SYS_get_thread_area failed with error: %s\n", strerror(errno));
        return 0;
    }
    else
    {
        mainThreadAddress[thrDescr._entry_number] = thrDescr._base_addr;
    }

    thrDescr._entry_number++;
    thrDescr._base_addr = 0x5555;
    res = syscall(SYS_set_thread_area, &thrDescr);
    if (res != 0)
    {
        printf("SYS_set_thread_area failed with error: %s\n", strerror(errno));
        return 0;
    }
    else
    {
        mainThreadAddress[thrDescr._entry_number] = thrDescr._base_addr;
    }

    //TLS_SET_GS_REG((7<<3)+3);
    for (unsigned long i = 0; i < NTHREADS; i++)
    {
        pthread_create (&h[i], 0, thread_func, (void *)i);
    }
    for (unsigned long i = 0; i < NTHREADS; i++)
    {
        pthread_join (h[i], 0);
    }
    for (unsigned long i = 0; i < NTHREADS; i++)
    {
        printf("%s", buf[i]);
    }
    return 0;
}

